Described below are a method for communication in a radio communication system in which a frequency band divided into a plurality of subcarriers is used and messages are transmitted in a plurality of hops and radio stations for carrying out the method.
In radio communication systems messages, for example containing voice information, image information, video information, SMS (Short Message Service), MMS (Multimedia Messaging Service) or other data, is transmitted between sending and receiving radio stations by a radio interface using electromagnetic waves. Depending on the specific configuration of the radio communication system the radio stations can be different types of subscriber-side radio stations or network-side radio stations such as repeaters, radio access points or base stations in this connection. In a mobile communications system at least some of the subscriber-side radio stations are mobile radio stations. The electromagnetic waves are emitted at carrier frequencies which are in the frequency band provided for the respective system.
Mobile communications systems are often constructed as cellular systems, for example according to the GSM (Global System for Mobile Communication) or UMTS (Universal Mobile Telecommunications System) standards with a network infrastructure having, for example, base stations, devices for monitoring and controlling the base stations and further network-side devices. Apart from these cellular, hierarchical radio networks that are organized over a wide area (supralocal) there also exist wireless local networks (WLANs, Wireless Local Area Networks) with a radio coverage range that is usually much more strongly physically delimited. Examples of different standards for WLANs are HiperLAN, DECT, IEEE 802.11, Bluetooth and WATM.
A connection to other communication systems, thus for example to the Internet, can take place via the WLAN radio access points. For this purpose the radio stations of the WLAN communicate either directly with a radio access point or via other radio stations with more remote radio stations which forward the information between the radio station and the radio access point via a path between the radio station and the radio access point.
Radio stations can only communicate with each other directly if they are both in the radio coverage range of the respective other radio station. If direct communication is not possible, messages can be transmitted between these radio stations via other radio stations, which, by forwarding the messages, act as relay radio stations. Message forwarding of this kind can, as a function of the specific configuration of the radio communication system, be carried out by subscriber-side and network-side radio stations. Messages can be forwarded for example in a WLAN between a radio access point and subscriber-side radio stations that are a long way from the radio access point in a plurality of hops. Subscriber-side radio stations can also communicate with each other in one or more hop(s) (hop or multihop) in an ad hoc mode of a radio communication system without intermediate devices, such as base stations or radio access points having to be connected in series. With a message transmission from a subscriber-side radio station to a further subscriber-side radio station outside of its radio coverage range the messages are forwarded by other subscriber-side radio stations which thus act as relay radio stations.
To achieve optimally efficient transmission of data the entire available frequency band is divided into a plurality of subcarriers (multicarriers or multicarrier method). The idea underlying the multicarrier system is to transform the initial problem of transmitting a broadband signal into the transmission of a plurality of narrowband signals. This has the advantage inter alia that the complexity required at the receiver may be reduced. The division of available bandwidth into a plurality of narrowband subcarriers also allows a much higher granularity of data transmission with respect to the distribution of the data to be transmitted among the different subcarriers, i.e. the radio resources can be distributed among the data to be transmitted or subscriber's stations with a high degree of fineness. The available bandwidth can be efficiently utilized by way of allocation of a number of subcarriers to different subscriber-side radio stations in particular with transmissions with variable data rates or with burst-like data traffic.
OFDM (Orthogonal Frequency Division Multiplexing) is an example of a multicarrier transmission method in which pulse forms that are approximately rectangular over time are used for the subcarriers. The frequency spacing of the subcarriers is chosen such that in the frequency space in the case of the frequency at which the signal of a subcarrier is evaluated the signals of the other subcarriers have a zero point. The subcarriers are therefore orthogonal to each other. As a result of the usually very small spacing of the subcarriers and the narrowband nature of the signals transmitted on the individual subcarriers, with OFDM it should be ensured that the transmission within the individual subcarriers is, in general, not frequency-selective. This simplifies signal equalization at the receiver.